Data Flow 2

In short

This is for many students a particularly hard assignment, so be sure to start on time. The assignment may be done alone or, preferably, in pairs. Every student should be able to explain orally and clearly every part of the assignment he hands in. The lecturer has the freedom to ask this explanation at any time, meaning that you might not be warned in advance).

Both parts of the assignment have equal weight in the final grade.

The goal of the assignment

To get a really thorough understanding of what is really happening in Chapter 2, you shall work on the following subjects:

• How to prove a soundness result for an analysis
• How to deal with the extension for procedures

Sometimes I ask you to give an illustrative, but small example. The idea is that your example should be as varied and broad as possible, but on the other hand should be as concise as possible. For instance, in the case of Strongly Live Variables (see below), I expect an example where a variable is strongly live, one which is not, one which is live but not strongly live, and maybe you can think of other cases. The bottom line is that your example is an alternative for a soundness proof, so the more convincing your example, the more convinced people will be (actually, a proof also only does the job when it is convincing).

The general rule is: Motivate your answers

The various parts of the assignment

Part 1: prove a soundness result.

Hint: It may surprise you that Lemma 2.16 does not hold in this case. Explain in your answer why that is, and modify the analysis so that it does hold and then continue.

Do Mini Project 2.2 on page 133.

Part 2: procedures and context

Do Exercise 2.18 for the Live Variable analysis. Work out the fibonacci example of Example 2.42 (page 103) by giving the resulting embellished monotone framework with context being call strings bounded by length k=2. (Beware: there are a few snakes in the grass here.) Remark: you do not have to work out the iteration itself. Be very precise when you give the transfer functions, especially those for call and return.

What, how and when to submit

Details can be found here. In whatever fashion you hand things in make sure things are clear and readable and on time. Make sure that you motivate your answers.

Experiences from last year

Part one is one many that students at first find difficult to do. Do not be fooled to believe that the proof is a copy of that in the book: it follows the same line, but what you actually have to prove is quite different, and asks for a different point of view. In practice it turned out that most students did this well.

Part two is also quite difficult, and people tend to forget quite a few details here. The main complication is how to simulate scoping. Even if you are unable to give complete formal details, be sure to explain how you conceptually can solve the problem. This already gets you quite a few points.

-- JurriaanHage - 14 Nov 2008